No. 2.] FCETAL MEMBRANES OF THE MARSUPIALS. 377 



In the following description there are necessarily gaps in the 

 determination of the various embryonic layers of which the 

 foetal membranes are composed, which can only be filled by 

 the observation of the stages intermediate between those of the 

 mid and final periods of uterine life. This, I trust, will be done 

 by Selenka. The same obtains of the physiology of that por- 

 tion of the chorion which is not attached to the uterine wall, 

 and of the fate of the allantois. 



About March ist a number of female opossums were 

 brought into the laboratory. In one, the young had been 

 recently born, transferred to the pouch, and then probably 

 destroyed by the mother at the time of capture. The nipples 

 were drawn out and the mammary-glands distended, but 

 the pouch was empty. Both uteri were laid open, and the 

 foetal membranes were found crowded into the uterine ori- 

 fices of the vaginae, which indicates that they had been 

 detached from the embryos in the uterus itself. No mem- 

 branes were found in the vaginae. A second female was then 

 examined. The pouch had been distended and moistened 

 for the reception of the young by the mother, but the nipples 

 were sessile. The uteri contained nine embryos each, which 

 by size and weight were obviously in the latest stage of develop- 

 ment. The free cavity of the uterus was filled with a clear, 

 thick fluid, which coagulated rapidly when the alcohol was 

 admitted. The condition of the mucous lining of the uterus at 

 this stage is very interesting, extensive changes having taken 

 place since the mid-period of development. As described in 

 my earlier paper, the inner wall of the uterus at the mid-period 

 presented one or two long parallel furrows faintly defined upon 

 its ventral surface, in which the embryos were ranged in a 

 single row, with the portion of the subzonal membrane to 

 which the yolk-sac is attached lying fixed in the furrow, the 

 remainder of the membrane lying free in the dorsal cavity. 



At this advanced period the mucous lining is reflected into 

 prominent folds, which in general have a circular arrangement, 

 greatly increasing the surface area, and serving to enfold the 

 large discs of the yolk-sac placentcs. The interior of these 

 folds is richly vascular, and the epithelium covering them is 

 altogether similar to that of the non-reflected surfaces (Fig. 4). 

 The walls of the uterus, in section, show the following rela- 



